Cylindrical air cell

Abstract: This invention is to improve the sealing of the top and/or bottom of cylindrical positive electrode of air-cell, and to prevent the leakage of electrolyte from the gelied zinc negative electrode disposed within the positive electrode which is constituted of a collector layer, catalyst layer, and a porous layer. By utilizing a positive electrode constituted of a metallic collector layer made of metal mesh or such, a catalyst layer disposed around said collector, and fluororesin porous layer, as an air electrode, an outer cup and an inner cup are pressed on the top of the positive electrode in order to prevent the leakage of electrolyte. The possible leakage of electrolyte from the bottom of positive electrode can be prevented by providing a resin sealing body with a ring-shaped indentation fitted to the bottom of positive electrode, and by inserting this resin sealing body into the positive electrode canister, and by pressing the side wall of positive electrode canister against the side of resin sealing body in order to fit the bottom of positive electrode to the indentation of resin sealing body.

Description: FIELD OF THE INVENTION This invention relates to a cylindrical air-cell of which top of positive electrode containing electrolyte and cathode active material or sealing of the bottom of said air-cell is made liquid tight. BACKGROUND OF THE INVENTION A structure of conventional cylindrical air-cell is explained below by referring Fig. 7 which shows a partly cutout side view of said air-cell. In Fig. 7, 101 is a cylindrical negative electrode containing an active material of so-called "gelied zinc" in which zinc powder is dispersed in gelied electrolyte, and 102 is a collector provided at the center of negative electrode 101. 103 is a multi-layered cylindrical positive electrode comprised of catalyst layer 104 containing manganese oxide and carbon material, collector layer 105 buried within catalyst layer 104, and a water-repellant porous layer 106 made of fluororesin contacted with a surface of catalyst layer 104. The other surface of said catalyst layer 104 is faced to negative electrode 102 through separator 107, and is operated by utilizing the oxygen contained in air as an active material. 108 is a cylindrical positive electrode-can containing air-diffusing layer 108 made of non-woven fabric covering the surface of said positive electrode 103, and other electricity generating elements including negative electrode 101 and positive electrode 103, and is provided with air-intake hole 110. 111 is an insulation tube covering the entire surface of said cylindrical positive electrode can 109, provided with air-intake hole 110 and air-intake window 112 which are connected to said air-intake hole 110. 113 is a seal closing said air-intake window 112 and 114 is a resin seal to which the bottom of positive electrode can 109 is bent and clamped. 115 is a bottom plate of the negative electrode terminal contacted with collector 102, 116 is a positive electrode cap-terminal contacted with the top of positive electrode 103, 117 is a cell cover, 118 is a grooved part, and 119 is a sealing material preventing the leakage of electrolyte. Explaining this cell structure further, the upper edge of positive electrode 103 is inwardly bent at the rim of grooved part 118, and the bent part is contacted with the rim of positive electrode cap-terminal 116, and these are inserted into cell-cover 117, and the upper edge of positive electrode canister 109 is bent and clamped at the rim of cell-cover 117. The lower edge of positive electrode 103 is sealed by inserting the bottom of water repellant porous layer 106 of positive electrode 103 between the sealing body 114 and the positive electrode canister 109, and clamped. By employing the above explained cell-structure, leakage of gelied electrolyte filled within the cylindrical positive electrode 103 and leakage of electrolyte containing the zinc powder filled in the negative electrode from the top to the bottom end of positive electrode canister 109 can be prevented. However, when the top end of cylindrical positive electrode 103 consisted of collector 105, catalyst layer 104, and water repellant porous layer 106, is bent at a rim of groove 118 provided for the sealing, clacks of catalyst layer 104 may apt to be produced at the bending or wrinkles of water-repellant porous layer 106 are apt to take place, and as a result of this, complete seal of cell-cover 117 had been hard to accomplish. Furthermore, since the sealing of bottom edge of positive electrode canister 109 is performed by clamping only the edge of water repellent porous layer 106 between the sealing body 114 and the positive electrode canister 109, clacks of edge of water repellent porous layer 109 are apt to be produced so that perfect seal had been hard to obtain. Since the alkaline electrolyte has a strong tendency of creeping and leakage through minute wrinkles or cracks of seal if produced, leakage of electrolyte may takes place easily during the storage period or during the usage thereof. Moreover, the conduction from positive electrode 103 to positive electrode canister 109 is performed by the mechanical contact of positive electrode 103 and positive electrode cap terminal 116 accomplished by the bending of the top rim of positive electrode canister 109, these contacts may become unstable by vibration or shock applied on the cell, making the electric-current supply unstable. FR-A-2152973 discloses in general terms a cylindrical positive electrode for a cell structure in which the top portion of the electrode is disposed between inner and outer cup shaped elements. SUMMARY OF THE INVENTION The present invention provides a cylindrical air-cell provided with a cylindrical positive electrode comprising a metallic collector layer, a catalyst layer disposed on the side wall of said metallic collector, and a porous layer disposed on an external surface of said catalyst layer; wherein an outer cap-shaped metal cup is fitted to the outside wall of an upper edge of said porous layer and an inner cap-shaped metal cup is fitted to the inner side wall of upper edge of said catalyst later; said positive electrode is housed in a cylindrical positive electrode canister equipped with a terminal part on its top; said terminal part and said outer cup are welded together; and an outer rim of said outer cup located outside of a part at which said terminal part and said outer cup are welded together and the inner rim surface of the positive electrode canister opposing to said outer rim of said outer cup are insulated from each other. In one embodiment the metallic collector layer is cylindrical and has a bent part formed on the top edge of said collector layer by bending the upper edge of the collector layer inwardly. Further, a protrusion may be provided at the top of the outer metal cup, the protrusion being welded onto the internal surface of the positive electrode canister. Further, a gas diffusion layer may be disposed between the porous layer and the electrode canister. In this arrangement, the gas diffusion layer may comprise a non-woven fabric disposed between the outer rim of the outer cup and the outer surface of the porous layer and the internal surface of the positive electrode canister. Alternatively, the gas diffusion layer may comprise a heat shrinking porous resin tube having a high air permeability disposed between the outer rim of said outer cup and outer surface of porous layer and the internal surface of said positive electric canister. In this arrangement, the air-cell may comprise openings provided on the side wall of the heat shrinking resin tube. This invention thus offers a new air-cell structure by which the top and bottom of the cylindrical positive electrode consisted of collector and catalyst layers and water-repellant porous layer are sealed liquid tight, preventing the external leakage of electrolyte held within the positive electrode. According to the above described explanations, the functions of the inventions are as follows. The top of a positive electrode consists of a metallic collector layer, a catalyst layer disposed on the side of said collector layer, and a porous layer held between two metal cups of different inner diameters, and the sides of said metal cups are pressed against said positive electrode, and by this, the top of said positive electrode can be completely sealed without producing cracks or wrinkles possible on said positive electrode so that the leakage of electrolyte from the top of positive electrode can be completely prevented. High electrical conductivity between the positive electrode and the metal cups can be obtained by employing a cylindrical collector layer of which top rim is inwardly bent, and by welding the bent rim to the inner wall of said outer cup, and by pressing said outer cup and inner cup to said bent rim of collector. Moreover, a high electrical conductivity or low internal cell resistance can be obtained by welding the top of said outer cup to the inner wall of said positive electrode canister, preventing contact failures between the collector and the cups even if unexpected shocks or vibration are applied to the cell. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a side view of the partly cut-off cylindrical zinc air-cell which is a first embodiment of the invention. Fig. 2 shows an enlargement of the part-A of Fig. 1. Fig. 3 shows an enlarged cross-section of the top edge of modified positive electrode of the cylindrical zinc air-cell shown in Fig. 1. Fig. 4 shows a top view of the outer cup of cylindrical zinc air-cell shown in Fig. 1. Fig. 5 shows a cross-section of the outer cup of cylindrical zinc air-cell shown in Fig. 4, sectioned at Line A-B. Fig. 6 shows an enlarged cross-section of the top edge of positive electrode of the cylindrical zinc air-cell which is a second embodiment of the invention. Fig. 7 shows a side view of the partly cut-off conventional cylindrical zinc air-cell. DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment-1) Fig. 1 shows a side view of the partly cut-off cylindrical zinc air-cell which is a first embodiment of the invention, Fig. 2 shows an enlargement of the part-A of Fig. 1, and Fig. 3 shows an enlarged cross-section of the top end of modified positive electrode of the cylindrical zinc air-cell shown in Fig. 1. In Figs. 1 to 3, 1 is a cylindrical negative electrode in which an active material of so-called gelied zinc and collector 2 are incorporated, 3 is a multilayered cylindrical positive electrode comprised of a catalyst layer 4 employing manganese oxide and carbon materials as main elements, collector layer 5 consisted of nickel plated stainless steel mesh disposed within catalyst layer 4, and a water-repellant porous layer 6 consisted of fluororesin contacted with a surface of catalyst layer 4, 7 is a separator disposed within catalyst layer 4 of positive electrode 3, within which negative electrode 1 is disposed, 8 is an air diffusion layer made of non-woven polypropylene fabric, 9 is a positive electrode canister on which positive electrode cap terminal 16 is integrally molded at its top, 10 is an air-intake hole provided on the positive electrode canister 9, 11 is an insulation tube, 12 is an air-intake window provided on insulation tube 11, 13 is a seal sealing the air-intake window until the cell operation, 14 is a seal made of resin, 15 is a bottom plate for negative electrode terminal, 17 is a sealing material, and 18 is a base paper. The manufacturing process of positive electrode 3, is began with a spot welding process overlapping the both ends of long collector layer forming collector 5 into a cylindrical shape and placing the overlapped part at a surface common with the side surface of collector 5, and a preformed catalyst layer 4 is then pressed on the both surfaces of cylinder-shaped collector 5. The material of catalyst layer 4 is prepared by mixing activated carbon, manganese oxide, acetylene-black, and fluororesin powder at a predetermined mixing ratio, and by further kneading of the mixture after a proper amount of ethylalcohol is added. Then, this kneaded mixture is extruded into a strip sheet having a thickness of about 0.6 mm. Said manganese oxide is prepared by applying a heat-treatment on γ-MnOOH in a nitrogen atmosphere at a temperature of 400°C, and said fluororesin powder is derived from polytetrafluoroethylene (PTFE) resin. Granulated or chained activated carbon having a particle diameter of 10 to 40 microns is used in this case. On the other hand, a fluororesin dispersant containing PTFE resin is coated on a surface of catalyst layer 4 and is dried at a temperature of 230°C. By this, the electrolyte can be easily permeated into the electrode, and obstruction of oxygen gas supply to the positive electrode can be prevented. The reason of the employment of a drying temperature of 230°C is to disperse the surface active agent contained in the dispersant. A gas-permeable water-repellant fluororesin layer is then pressed on the surface coated with fluororesin dispersant in order to obtain porous layer 6 of positive electrode 3 act as an air electrode. Thus prepared positive electrode 3 is wound involute in a form of cylinder to face catalyst layer 4 inwardly. Then, inner cup 20 and outer cups 19 both made of nickel plated steel plate are disposed on the top of cylindrical positive electrode 3, so that outer cup 19 is contacted with the outer rim while inner cup 20 is contacted with the inner rim of the top edge of said porous layer 5. As a result of this, positive electrode 3 can be sealed at a condition where the top edge of positive electrode 3 is held between the outer cup 19 and inner cup 20. Since the outside of outer cup rim is grooved by using a roller and is pressed against the outer surface of positive electrode 3 while inner cup 20 is widened within a space of catalyst layer 4 and pressed against the inner wall of positive electrode 3, positive electrode 3 is held and clamped between the inner cup 20 and the outer cup 19 forming an air-tight and leakage-free sealing. Furthermore, as shown in Fig. 3, the entire inner surface of outer cup 19 is coated with a synthetic rubber sealing material made mainly of chlorosulfonated-polyethylene for example forming a sealing layer 22, in order to improve the air-tightness and leakage-proof performance realizing high reliability of the sealing. Thus, after sealing the top of positive electrode 3, the external surface of porous layer 6 and the area from the outer rim of outer cup 19 to the upper round-off part are wrapped by air-diffusion layer 8. As shown in Figs. 4 and 5, small protrusions 23 are disposed on the external top surface of outer cup 19 at three points avoiding a straight line disposition, and these small protrusions 23 are spot-welded on the inner surface of terminal 16 of positive electrode cap, disposed on the top of positive electrode canister 9. Moreover, the top of said air-diffusion layer 8 is disposed between the outer rim of outer cup 19 located outside of said small protrusions 23 and the inner side surface of positive electrode canister 9 opposing to these protrusions in order to avoid the contact of outer cup 19 to positive electrode canister 9. By employing the above-described cell construction, since the eddy current produced at welding of small protrusions onto the top inner surface of positive electrode canister 9 is concentrated only to the small protrusions of outer cup 19, a higher welding strength and better appearance welding between the positive electrode canister 9 and the small protrusions can be obtained. Moreover, because of an opening 21 provided on the top center of inner cup 20, a welding rod can be inserted through opening 21 when positive electrode canister 9 is welded to the outer cup 19 so that the welding bar can be contacted with outer cup 19 and the welding of these components can be performed easily at a better stabilized condition. Furthermore, instead of the non-woven fabric, air diffusion layer 8 covering the outside surface of porous layer 6 and the area from the outer side surface to the top of cup 19 can be formed by using a heat-shrinking porous resin tube made of a resin material such as air-permeable PET or a heat shrinking tube with small openings prepared in advance. The bottom edge of positive electrode 3 is formed by bending the bottom edge of positive electrode 9 against the rim of sealing body 14 and by clamping, and by placing the lower edge of porous layer 6 between the sealing body 14 and the positive electrode canister 9 and by filling the gap with a sealing material 17. Ten of the cylindrical zinc air-cells A are constructed according to Embodiment-1 shown in Fig. 1, ten conventional cylindrical zinc air-cells C are constructed by bending the top edge of positive electrode inwardly and contacted with the bent part as shown in Fig. 14. Ten cylindrical zinc air-cells B are constructed according to Embodiment-1 shown in Fig. 3 but with sealing layer 22 is formed on the inner surface of outer cup 19, and ten conventional cylindrical zinc air-cells D with sealing layer 22 formed at the top edge of positive electrode, are prepared. The storage characteristics of these cells are comparatively tested at a storage temperature of 60°C and the result of these are shown in Table 1. Storage Period (at 60°C) Tested cells Sealing applied on outer cup 1 week 2 weeks 3 weeks 1 month Cell A (Fig. 1) None 2/10 8/10 10/10 - Cell B (Fig. 3) Yes 0/10 0/10 0/10 0/10 Cell C (conventional) None 10/10 - - - Cell D (conventional) Yes 10/10 - - - As shown in Table 1, the conventional zinc air-cells C and D showed very severe electrolyte leakages within very short periods, regardless the coating of sealing material. On the other hand, none of the zinc air-cells B of Embodiment-1 showed leakage after a storage period of one month at 60°C while all of the zinc air-cells A showed leakage after a storage period of three weeks. Therefore, significant improvements of leakage stopping characteristics obtained by the invented zinc air-cells over those of conventional zinc air-cells are confirmed, in addition to further improvements obtained with sealing layer 22 formed on the internal surface of outer cup 19. However, when the width of overlapped region of the cylindrically formed collector is inadequate, an insufficient tensile strength of the overlapped region would be produced. Therefore, when a volume expansion of the zinc negative electrode 1 is produced at discharge, breakage of welded points at the edges of collector may takes place, causing electrolyte leakage. Thus, at least an overlap width of 1.3 % of the circumference of collector layer 5 have to be provided. On the other hand, when said overlapped width is too large, the collector area providing minute holes are plugged, sacrificing the discharge capacity somewhat. The sacrifice of discharge capacity can be minimized by setting the overlapped width at less than 9% of the total circumference of collector layer 5. Although a case where the both ends of long stainless steel mesh strip are over-lapped to constitute a cylindrical collector is shown here, the collector of the same function can be obtained by weaving a long horizontal metal thread into a number of independent vertical fine metal wires formed into a shape of cylinder. Both the horizontal and vertical metal wires in this case, could be nickel plated stainless steel wire or nickel wire, and in this case, erosion of collector by the alkaline electrolyte can be minimized so that the storage characteristics of cell can be improved. (Embodiment-2) A bent part 24 formed by bending the top edge inwardly is provided on cylindrical collector 5 as shown in Fig. 6. By pressing and fitting outer cup 19 onto both the upper surface of bent part 24 and the upper edge rim of porous layer 6, and by pressing and fitting the inner cup 20 onto both the lower surface of bent part 24 and the inner rim of upper edge of catalyst layer 4, the bent part 24 can be held and clamped between the inner cup 19 and the outer cup 20. At this condition, outer cup 19 and bent part 24 can be welded together. A cylindrical air-cell according to the above shown cell construction yet having a cell construction identical with those shown in Fig 1 for the rest of the cell, is fabricated, and this cell is named as cell E of the embodiment of the invention. Ten each of Cells E and A are prepared and the internal cell resistances are determined, and the results of these are listed in Table 2. Right after cell assembly (in Ω) After 20 day storage at 60°C (in Ω) Invented Cell-E (Fig. 6) x 0.154 x 0.186 Max 0.17 Max 0.20 Min 0.14 Min 0.16 σ n-1 0.010 σ n-1 0.015 Invented Cell-A (Fig. 1) x 0.216 x 0.352 Max 0.27 Max 0.37 Min 0.18 Min 0.31 σ n-1 0.216 σ n-1 0.024 As shown in Table 2, substantial decreases of the internal resistance resulted from the closer contacts of bent part 24 of collector layer 5 to outer cup 19 and inner cup 20 is proved by cell E which is an embodiment of the invention. This result proved that the internal resistance can be kept at low even after a storage period of 20 days at 60°C. The advantages of cell E have been confirmed with the cells assembled by using no welding of bent part 24 to collector layer 5 but is merely held between these two elements. As above explained so far, the cylindrical air-cell of the invention consists of a metallic collector layer, a catalyst layer disposed on the side of said metallic collector layer, and a porous layer acting as a cylindrical air electrode disposed on the outside of said catalyst layer, and is provided with an outer metal cup pressed on the outer top edge of said positive electrode and an inner metal cup pressed on the inner top edge of said positive electrode. Since the top of positive electrode is pressed and clamped by said outer and inner cups, the sealing of the top of positive electrode can be substantially improved, offering air-cells having excellent sealing and leak-proof characteristics. Moreover, by providing a bent part at the top edge of metallic collector layer, by holding and clamping said bent part against between said outer metal cup and inner metal cup, and by welding said collector layer and outer cup, the contacts between these elements can be held at a best condition, nullifying the possibility of internal resistance increase due to poor contacts between the collector layer and the outer and inner cups. Furthermore, a resin mold body having a ring-shaped indentation fitted to the lower edge of positive electrode is disposed at the bottom of positive electrode, and after said resin mold body is inserted into the positive electrode canister, the side of said positive electrode canister is inwardly pressed against the side of said resin mold body in order to improve the sealing between the bottom of positive electrode and the ring-shaped indentation of said resin mold body, thus improving the leak-proof characteristics of the bottom of positive electrode.

Claims: A cylindrical air-cell provided with a cylindrical positive electrode (3) comprising a metallic collector layer (5), a catalyst layer (4) disposed on the side wall of said metallic collector, and a porous layer (6) disposed on an external surface of said catalyst layer (4); wherein an outer cap-shaped metal cup (19) is fined to the outside wall of an upper edge of said porous layer (6) and an inner cap-shaped metal cup (20) is fitted to the inner side wall of upper edge of said catalyst later (4); said positive electrode (3) is housed in a cylindrical positive electrode canister (9) equipped with a terminal part (16) on its top; said terminal part (16) and said outer cup (19) are welded together; and an outer rim of said outer cup (19) located outside of a part at which said terminal part (16) and said outer cup (19) are welded together and the inner rim surface of the positive electrode canister (9) opposing to said outer rim of said outer cup (19) are insulated from each other. A cylindrical air-cell according to Claim 1 in which said metallic collector layer (5) is cylindrical and has a bent part (24) formed on the top edge of said collector layer by bending the upper edge of said collector layer inwardly. A cylindrical air-cell according to Claim 1 or 2 wherein a protrusion (23) is provided on the top of said outer metal cup (19), and said protrusion is welded on the internal surface of said positive electrode canister (9). A cylindrical air-cell according to Claim 1, 2 or 3 in which a gas diffusion layer (8) is disposed between said porous layer (6) and said electrode canister (9). A cylindrical air-cell according to Claim 4 in which said gas diffusion layer (8) comprises a non-woven fabric disposed between the outer rim of said outer cup (19) and outer surface of said porous layer (6), and internal surface of said positive electrode canister (9). A cylindrical air-cell according to Claim 4 in which said gas diffusion layer (8) comprises a heat-shrinking porous resin tube having a high air permeability disposed between the outer rim of said outer cup (19) and outer surface of porous layer (6), and internal surface of said positive electrode canister (9). A cylindrical air-cell according to Claim 6 in which openings are provided on the side wall of said heat-shrinking resin tube.

Inventors: EDA NOBUO, FUJIWARA TAKAFUMI, KUBO ISAO, MIURA AKIRA, NOYA SHIGETO, YOSHIZAWA HIROSHI, EDA, NOBUO, FUJIWARA, TAKAFUMI, KUBO, ISAO, MIURA, AKIRA, NOYA, SHIGETO, YOSHIZAWA, HIROSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H01M12
IPC codes: H01M2, H01M12, H01M4